1. Field of the Invention
The present invention relates to sandwich glass. More particularly, it relates to a sandwich glass comprising a glass plate with one or more glass plates or hard plastic sheets which are united through a soft interlayer, which is useful as window glasses, lightening materials, sheltering materials, etc. in various fields, especially, as front glass of cars, window glass of vehicles such as aeroplanes, electric cars, etc. or window glass of skyscrapers.
2. Description of the Prior Art
Recently, it is recommended to use sandwich glass as front glass of cars, in view of safety, instead of partially tempered glass hithertofore used, and sandwich glass is nowadays employed for not only quality cars but also public cars. Such sandwich glass is called as safety glass, which consists of usually two or more glass plates laminated and united through soft resin as interlayers. Accordingly, in the case of such sandwich glass, even if the glass plate is damaged by affection of external force, the impact is absorbed by the interlayer and hence the majority of broken glass pieces do not scatter.
As the resin interlayer for the sandwich glass, plasticized butyral resins are mainly used at present, although synthetic resins of cellulose nitrate series or cellulose acetate series have been used hithertofore. The sandwich glass is usually produced by heating the resin interlayer held between glass plates under increased pressure or by heating it at high temperature under reduced pressure while removing air-bubbles.
The plasticized butyral resins mentioned above exhibit excellent properties as interlayer, but show the the drawbacks of a high specific gravity and a fairly lowered impact-absorbing ability, because they become remarkably hard and brittle at low temperatures, especially, below -20.degree. C. Therefore, sandwich glass using such plasticized butyral resins as interlayer includes problems in its weight and its effectiveness as used in cold district.